Vertical organic transistors are semiconductor components having three electrodes. In particular organic molecules, carbon compounds and polymers are used as semiconducting layers. The device has a plurality of superposed planar layers which are fabricated on a substrate. Since the currents in the device flow perpendicular to the functional layers and therefore also to the device, it is designated as vertical device.
The following tasks or functions are ascribed to the vertical organic transistor: amplifying currents and/or voltages, electrical switches in order to control the current flow through subsequent devices, executing logic operations in combination with a plurality of devices and various tasks of analogue signal processing.
An advantage of organic transistors with vertical current flow lies in the short length between the electrodes, which can be adjusted very accurately by means of vapour deposition of materials in vacuum. This reduces the time required for a charge carrier to traverse the organic semiconductor. High switching speeds are thus obtained, these being required, for example, for the active triggering of screens with organic light-emitting diodes (OLED).
In addition, as a result of the small dimensions of a few hundred nanometres, even at low voltages, which typically lie below 5 V, very high electric fields are achieved. As a result, high current densities are achieved in the device, which are sufficient to bring a downstream OLED to application-relevant brightness. Furthermore, OLEDs are also designed so that the currents flow vertically to the substrate, and vertical organic transistors have the same architecture and are therefore suitable for being processed consecutively in a fabrication process. This results in a higher packing density and a higher proportion of the area of a screen which can contribute to the emission of information.
Known from the document US 2010/0213447 A1 is a vertical organic transistor in which a middle electrode is configured as a continuous layered body which contains an isolating metal compound and metal particles which are distributed in the insulating compound.
The document U.S. Pat. No. 6,884,093 B2 discloses an organic semiconductor device in which a middle electrodes in an organic layer arrangement is formed with a conducting grid material.
The document U.S. Pat. No. 6,774,052 B2 describes a method for fabricating a permeable base transistor in which a base layer is deposited in a semiconductor substrate and a semiconductor layer grows on the base layer, where the base layer comprises metal nanotubes.
Vertical organic transistors are further known as such from the following documents: Nakayama et al., Appl. Phys. Lett., 2006, 88, Cheng et al., Org. Electron., 2009, 10, Watanabe et al., Jpn. J. Appl. Phys., 2006, 45, Fujimoto et al., Appl. Phys. Lett., 2005, 87.
Applications at high frequencies and high current densities have also been described for organic vertical transistors (Fischer et al, Appl. Phys. Lett., 2012, 213303).
So-called mask technology can be used to fabricate a vertical organic transistor or circuit arrangements herewith. In this case, the device layers are deposited using mask structures which have one or more openings through which the respective layer is deposited in a desired area of the device. The accuracy of the layer deposition in a desired area depends in particular on the tolerances of the mask structure itself as well as the positioning accuracy of the mask structure. As a result, defective structures occur, particularly in the outer edge region of the vertical organic transistor to be fabricated, in which the desired layer overlap is defective. For example, it can occur that the control electrode (middle electrode) of the transistor only overlaps with an organic layer on one side so that fault currents occur here which are not available for the correct operation of the transistor.